Advancements in technology and processes related to memory device fabrication have enabled continued scaling down (size reduction) of memory devices. As a memory device is scaled down, memory density is increased and the speed of the memory device is also increased. A contributory factor in the continuing scaling down of memory devices is the development of and introduction of STI (shallow trench isolation) into memory device fabrication.
Implementing STI (shallow trench isolation) in memory device fabrication has enabled developers to properly scale down the memory device and improve circuit density. State of the art memory devices are being fabricated utilizing shallow trench isolation in the core memory area, realizing an improvement in memory density. Additionally, employing STI in memory device fabrication also maintains critical properties of a memory device, such as data retention, charge leakage, and device reliability under high voltage programming/erase operations.
In memory device fabrication, one crucial process is the formation of the tunnel oxide. Tunnel oxide formation is closely coupled to STI related processes. During the formation of STI, the silicon can be damaged at the STI corner (where the edges are compressed) and at the edge. STI damage is more severe at the corner due to compressed edges causing crystal disruption and/or crystal dislocation. This leads to imperfect tunnel oxide edge formation which can cause oxide edge degradation. Oxide edge degradation is a contributing factor in reliability, charge retention, and leakage problems in memory devices.
Current testing devices, e.g., long finger structures, provide information regarding tunnel oxide formation based on electrical measurements of the edge portions of a memory device. However, in a practical application finger structures are not present. Accordingly, edge measurements alone do not provide adequate information with regard to the formation of the oxide, e.g., tunnel oxide, in a memory device, e.g., a flash memory device.
Thus, a need exists for an apparatus to provide more comprehensive measurements related to oxide formation. An additional need exists for an apparatus to include corner characteristics in the measurements related to oxide formation. Yet another need exists for an apparatus that provides those measurement in a simple manner and which is readily implemented during the fabrication of a memory device.